Formaldehyde resins, which for example are employed as impregnating solutions, are frequently not burnable or only poorly burnable themselves. Nevertheless, for many uses it is desirable that they be provided additionally with a fire retardant so that the substrate treated with the formaldehyde resin solution is made non-combustible.
Known fire retardants, which generally have a high content of nitrogen and phosphorus or their aqueous solutions have the disadvantage that they are not compatible with formaldehyde resin solutions, for example, novolaks dissolved in methanol.